The present invention relates to improved heat flow control in longitudinal discharge lasers, and more particularly, it relates to improved infrared heat flow control in metal vapor lasers.
Longitudinal discharge lasers have a number of uses. Specifically for metal vapor lasers, applications are known in uranium isotope separation using copper vapor and in the medical field using gold vapor. Other metal vapor laser media include lead and barium. An example of the use of copper vapor lasers to pump dye lasers for uranium isotope separation is describes in UCRL-88040 on Atomic Vapor Laser Isotope Separation by James I. Davis. This paper describes work done as of the Fall of 1982 with individual copper vapor laser pumped dye laser oscillators run over 1,000 hours in accumulated time. This lifetime test not only illustrates that copper vapor lasers act usefully as dye laser pump sources, but also that copper vapor laser lifetime is an important issue for atomic vapor laser isotope separation. Since the copper vapor lasers had to be stopped several times to replenish the copper supply, the copper vapor laser design employed in the 1,000 hour life test differs from the design needed for an isotope separation plant.
In the past, infrared radiation from the walls of a longitudinal discharge laser was not well controlled as it propagated past the electrode toward the window. Not only could infrared (IR) radiation travel directly down the laser axis and hit the window, but also IR radiation could strike the walls of the tube surrounding the laser and reflect to subsequently hit the window. Two examples showing the unobstructed path for IR radiation between the electrode and the window are U.S. Pat. No. 3,654,567 (FIGS. 1 and 2) and U.S. Pat. No. 4,247,830 (FIG. 1). In each case IR radiation emerging from the central discharge region of the laser past the electrode is free to hit the window directly or after reflection.
IR radiation striking the windows of a longitudinal discharge laser causes problems if the windows are made of a material which significantly absorbs in the infrared. A typical window material is quartz, which is an IR radiation absorber. The IR radiation striking the windows is then absorbed in part by the windows. This absorption causes heating of the window. As window material gets hotter, its index of refraction changes. Also, there can be some warping of the window. The effect is a focusing of the laser beam as if the window had turned into a very long focal length lens. This focusing can reduce the laser power emerging from a train of laser amplifiers by up to one half. A choice of non-IR absorbing materials for windows leads to other problems, so a reduction in window heating effects in IR absorbing materials, such as quartz is desired.